If they acquired New Relic and integrated it into the Heroku Dashboard it would give them another edge over normal hosting, but doubt that will happen. New Relic seems to do fine be themself.
New Relic is a bigger business now* (*speculating). And it used to be integrated into the dashboard before the add-on marketplace existed.
Heroku is owned by Salesforce so I doubt that. Interesting to know it used to integrate directly into Heroku before the addons though, didnt know that.